With computerization of documents and spread of World Wide Web (abbreviated as WWW), document search is becoming widely used in daily life and in various fields of business. The document search here refers to a technology of searching for various types of content according to a search request with a specified search keyword. Types of content to be searched for by the document search include, in addition to a document itself such as a reference material, various objects such as a web page including text data, video content including text data as metadata, and the like.
The search results by the document search are output as a list of titles of pieces of content matching the search keyword, for example. A user obtains desired information by performing, and repeating if necessary, the steps of inputting a search keyword, selecting a piece of content from a list of titles output as the search results and checking the piece of content.
Conventionally, various methods are being proposed to reduce the steps and save the trouble regarding the document search as described above, and to improve the work efficiency of a user. One of such methods is input completion of a search keyword (a suggestion function). The search suggestion function is a technology of acquiring, and presenting to a user, candidates for a search keyword whose written expressions or readings of Japanese partially match an input string. By using this search suggestion function, a user can issue a search request by selecting a search keyword from presented candidates, without having to fully input a search keyword, and the trouble of inputting a search keyword can be saved. However, with the search suggestion function, since candidates for a search keyword whose written expressions or readings of Japanese partially match that of an input string are presented to a user, if a plurality of search keywords that are different in the written expression or reading of Japanese are to be sequentially specified and the search is to be repeated, the input of a string has to be performed every time from the start.
As a method for saving the trouble of sequentially specifying a plurality of search keywords and repeating the search, there is known a technology of presenting, when a search keyword is input, together with search results based on the search keyword, other words related to the search keyword used for the search as the candidates for the next search keyword. According to this technology, a user can issue a new search request by selecting the next search keyword from the presented candidates for the search keyword, and the trouble of sequentially specifying a plurality of search keywords and repeating the search can be reduced. However, with this technology, candidates for the next search keyword cannot be presented until a search keyword is entered, and to cause other candidates related to a candidate for a presented search keyword to be presented, search has to be performed every time by entering a search keyword.
As described above, conventional technologies for reducing the steps of document search and saving the trouble has yet to be improved from the stand point of improving the work efficiency of a user, and a technology that can further improve the efficiency is desired.